Electromagnetic noise suppressor, structure with electromagnetic noise suppressing function and their manufacturing methods

ABSTRACT

An electromagnetic noise suppressor of the present invention has magnetic resonance frequency of 8 GHz or higher, and the imaginary part of complex magnetic permeability at 8 GHz is higher than the imaginary part of complex magnetic permeability at 5 GHz. Such an electromagnetic noise suppressor is capable of achieving sufficient electromagnetic noise suppressing effect over the entire sub-microwave band. The electromagnetic noise suppressor can be manufactured by forming a composite layer on the surface of a binding agent through physical deposition of a magnetic material on the binding agent. The structure with an electromagnetic noise suppressing function of the present invention is a printed wiring board, a semiconductor integrated circuit or the like that is covered with the electromagnetic noise suppressor on at least a part of the surface of the structure.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 10/538,132, filed Jun. 9, 2005, which is a U.S.C. §371 NationalPhase conversion of PCT/JP2004/002104, filed Feb. 24, 2004, the entirecontents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an electromagnetic noise suppressorthat suppresses electromagnetic noise, to a structure with anelectromagnetic noise suppressing function, and to a method ofmanufacturing the same.

BACKGROUND ART

In recent years, as the use of the Internet has increased, electronicapparatuses that use CPUs running at high clock frequencies in asub-microwave band (0.3 to 10 GHz), electronic apparatuses that use highfrequency bus, and telecommunication apparatuses that utilize radiowaves have been increasing, such as personal computers, home applianceshaving information processing functions, wireless LAN,bluetooth-equipped apparatuses, optical module, mobile telephones,mobile information terminals and intelligent road traffic informationsystem. This trend leads to a society of ubiquitous computing thatrequires devices of higher performance with high-speed digitalinformation processing function and low-voltage driving. However, assuch apparatuses become popular, concerns have been increasing on theproblems related to the electromagnetic interference such asmalfunctioning of an apparatus that emits electromagnetic radiation orother apparatuses and health threats to humans. For this reason, such anapparatus is required to minimize the emission of unnecessaryelectromagnetic radiation so as not to affect its own operation and thatof other apparatuses and so as not to cause adverse effects on the humanbody, and to operate without malfunctioning when subjected toelectromagnetic radiation emitted by other apparatuses. Measures toprevent such electromagnetic interference include the use of anelectromagnetic radiation shielding material that reflectselectromagnetic radiation and the use of an electromagnetic radiationabsorbing material.

As a means for preventing electromagnetic interference betweenelectronic apparatuses, electromagnetic radiation shielding material isprovided on the surface of the housing of the electronic apparatus orbetween the electronic apparatuses so as to block electromagneticradiation (inter-system EMC). As a means for preventing electromagneticinterference within an electronic apparatus, electronic components andcircuits are covered with electromagnetic radiation shielding materialso as to prevent the electronic components and circuits from interferingwith each other and resulting in malfunction, and suppressing theprocessing speed from decreasing and signal waveform from beingdistorted (intra-system EMC). Particularly in near-field environmentssuch as within an electronic apparatus, it has been required to suppressthe generation of electromagnetic noise by providing electromagneticnoise suppressing measures to electronic components that are the sourcesof the electromagnetic noise or to suppress the interference betweensignals thereby to improve the transmission characteristic (micro EMC).

Electronic apparatuses and electronic components are recently requiredto have higher performance and become smaller and lighter in weight, andthe electromagnetic noise suppressor used in these apparatuses orcomponents is also required to have high electromagnetic noisesuppressing effects in a high-frequency band such as a sub-microwaveband, be smaller and lighter in weight, and be easy to carry out by thework which takes measures with electromagnetic noise suppressingmeasures.

As the electromagnetic radiation shielding material, for example, anelectromagnetic noise suppressor including a mixture of two kinds ofsoft magnetic material powder having different mean particle sizes,namely soft magnetic material powder particles having morphologicalmagnetic anisotropy, that are dispersed in an organic binding agent isdisclosed in Japanese Patent Application, First Publication No. Hei9-35927.

In the publication described above, the electromagnetic noise suppressoris disclosed to have anisotropic magnetic fields of differentintensities so as to demonstrate a plurality of magnetic resonances anddifferent values of the imaginary part of complex magnetic permeability(μ″) that correspond to different frequencies are superposed, thusresulting in the distribution of the imaginary part of complex magneticpermeability (μ″) over a wide range of frequencies. The imaginary partof complex magnetic permeability (μ″) is a magnetic loss term requiredfor absorbing electromagnetic radiation, and it is said that highelectromagnetic noise suppressing effect can be achieved as theimaginary part of complex magnetic permeability (μ″) is distributed overa wide range of frequencies.

As another electromagnetic radiation shielding material, anelectromagnetic radiation absorbing material having a compositestructure of flake-shaped powder of iron nitride (Fe₁₆N₂) and a resin isdisclosed in Japanese Unexamined Patent Application, First PublicationNo. 2001-53487.

In the publication described above, it is described that, when themagnetic material has a high value of saturation magnetization Is, valueof fr(μ′−1) that represents the limit of magnetic permeabilityincreases, thus limitation line shifts toward higher frequency, so thathigher magnetic permeability is achieved at high frequencies. As aresult, it is claimed, that the use of iron nitride that has the highestsaturation magnetization among various magnetic materials enables it toachieve higher magnetic permeability at higher frequencies with theresonance frequency fr reaching about 5 GHz. It is also described thatthe resonance frequency can be freely varied in a range from severalhundreds of MHz to near 10 GHz by controlling the composition of theresin, heat treatment conditions, shape of the iron nitride particlesand/or aspect ratio. An example of application is shown where ICsmounted on a wiring board are covered, together with the leads thereof,with an electromagnetic absorbing material in the state of a paste.

As another electromagnetic radiation shielding material, a NiZn ferritethin film is known that can be used to suppress electromagneticinterference (EMI) in the sub-microwave band (Masaki ABE et al.,“Application of Thin Ferrite Film and Ultra-Fine Particles formed inAqueous Solution to Microwave/Nano-Biotechnology”, pp 721-729, No. 6,Vol. 27, 2003; Journal of The Magnetics Society of Japan).

This publication describes a NiZn ferrite thin film having the resonancefrequency increased to 1.2 GHz. It is also described that the NiZnferrite thin film is formed by plating on the surface of lead wires orsemiconductor devices of a circuit by spin spraying process, and theNiZn ferrite thin film absorbs noise current before electromagneticnoise is generated from the noise current.

However, the electromagnetic interference suppressor (JapaneseUnexamined Patent Application, First Publication No. Hei 9-35927) thatis claimed to have imaginary part of complex magnetic permeability (μ″)distributed over a broad range of frequencies is made by simplyincreasing the imaginary part of complex magnetic permeability (μ″)partially, as indicated by the μ-f characteristic diagrams of FIG. 2 andFIG. 3 of this publication, and has magnetic resonance frequency lowerthan 2 GHz. Also the values of the imaginary part of complex magneticpermeability (μ″) shown in the μ-f characteristic diagrams are onlythose for frequencies up to 2 GHz, thus it is impossible to provesufficient electromagnetic noise suppressing effect over the entiresub-microwave band.

With regards to the electromagnetic radiation absorbing material havingcomposite structure of flake-shaped powder of iron nitride and a resindisclosed in Japanese Unexamined Patent Application, First PublicationNo. 2001-53487, it is described that flake-shaped powder of iron nitride(Fe₁₆N₂) in quasi stable structure is made by thin film forming processsuch as vacuum vapor deposition, sputtering, CVD, MBE or the like,although details are not known since no examples are described. However,it is difficult to stabilize the crystal structure of iron nitride(Fe₁₆N₂), and iron nitride of stable structure is also included. Thus itis difficult to make flake-shaped powder of iron nitride (Fe₁₆N₂) thathas sufficiently high saturation magnetization. It is also verydifficult and impractical to make flake-shaped or disk-shaped finepowder of iron nitride (Fe₁₆N₂) by using a mask. It is described thatthe resonance frequency can be varied up to near 10 GHz by controllingthe composition of the resin, heat treatment conditions, shape of theFe₁₆N₂ particles and/or aspect ratio. However, examples are given onlyfor those having resonance frequencies up to about 5 GHz (FIG. 5 ofJapanese Unexamined Patent Application, First Publication No.2001-53487), and there remain problems in practical application.

Although resonance frequency of the NiZn ferrite thin film proposed byABE et al. is made higher, it is below 2 GHz and is not sufficient foran electromagnetic noise suppressor used in sub-microwave band. Also,this publication gives the values of the imaginary part of complexmagnetic permeability (μ″) only for frequencies up to 3 GHz in thecomplex magnetic permeability spectrum (FIG. 4), while the spectrum isabout to decrease at 3 GHz, indicating that the resonance frequencycannot increase further. The publication also shows the manufacture of aNiZn ferrite thin film by directly plating onto copper wires andsemiconductor devices of a circuit, as an example of application. Sincethe plating solution contains cations of Na, etc. and anions such aschlorine and nitrous acid, it requires careful cleaning when used forsemiconductor devices, resulting in increased number of operationprocesses.

When soft magnetic material powder or flake-shaped powder of ironnitride is used, it must be used in a large amount in order to achievesufficient electromagnetic interference suppressing effect andelectromagnetic radiation absorbing effect, the amount being usuallyabout 90% by weight of the electromagnetic interference suppressor andelectromagnetic radiation absorbing material. When soft magneticmaterial powder or flake-shaped powder of iron nitride is used, it isalso necessary to increase the thickness of the electromagneticinterference suppressor or the electromagnetic radiation absorbingmaterial in order to achieve sufficient electromagnetic interferencesuppressing effect and electromagnetic radiation absorbing effect. Thus,there has been a problem in that the electromagnetic interferencesuppressor or the electromagnetic radiation absorbing material has highspecific gravity and is thick, and is therefore heavy.

There has also been a problem in that the electromagnetic interferencesuppressor or the electromagnetic radiation absorbing material is thickand makes it difficult to reduce the space requirement.

The electromagnetic interference suppressor or the electromagneticradiation absorbing material also lacks flexibility and is brittle,since it is constituted mostly from the soft magnetic material powder orthe flake-shaped powder of iron nitride, with a small content of bindingagent.

With the background described above, an object of the present inventionis to provide an electromagnetic noise suppressor that has sufficientelectromagnetic noise suppressing effect over the entire sub-microwaveband, a structure such as printed wiring board or semiconductorintegrated circuit that is provided with electromagnetic noisesuppressing means and a method for easily manufacturing the same.

Another object of the present invention is to provide an electromagneticnoise suppressor that requires smaller installation space and is lighterin weight, flexible, and has high strength.

DISCLOSURE OF INVENTION

The present inventors considered that the way to achieve highelectromagnetic noise suppressing effect in the sub-microwave band is totransform noise current into thermal energy by means of the magneticloss characteristic of a magnetic material, which means that thematerial has sufficiently high value of the imaginary part of complexmagnetic permeability (μ″) (namely loss term) in this frequency band.After studying the integration of the binding agent and the magneticmaterial dispersed in the former in the atomic state so as to make useof the effect of magnetic anisotropy such as morphological anisotropy,the inventors developed an electromagnetic noise suppressor of highmagnetic resonance frequency that can be used in the sub-microwave band.

The electromagnetic noise suppressor of the present invention ischaracterized in that the magnetic resonance frequency is 8 GHz orhigher, and the imaginary part of complex magnetic permeability (μ″_(H))at 8 GHz is higher than the imaginary part of complex magneticpermeability (μ″_(L)) at 5 GHz. Such an electromagnetic noise suppressorcan demonstrate sufficient electromagnetic noise suppressing effect overthe entire sub-microwave band.

The electromagnetic noise suppressor of the present invention preferablyhas a composite layer formed by integrating the binding agent and themagnetic material. Such an electromagnetic noise suppressor can havemagnetic resonance frequency of 8 GHz or higher, and make the imaginarypart of complex magnetic permeability μ″_(H) at 8 GHz higher than theimaginary part of complex magnetic permeability μ″_(L) at 5 GHz, andenables it to reduce the space requirement and weight. In the case inwhich the composite layer is a layer formed by physicallyvapor-depositing the magnetic material onto the binding agent, thecomposite layer has such a constitution as the magnetic material isdispersed in the binding agent so that the magnetic material and thebinding agent are integrated with each other so as to provide highelectromagnetic noise suppressing effect. The composite layer does notcontain impurity ions so that there is no possibility of damage to theelectronic circuit by the impurity ions.

In the case in which the binding agent is a resin or rubber, theelectromagnetic noise suppressor can be made flexible and have highstrength.

If the binding agent is a hardening resin, the magnetic material can bedispersed more uniformly in the binding agent that has not yet cured.After the binding agent has cured, the magnetic material does notcrystallize into fine particles, and such a composite layer can beobtained as the binding agent and the magnetic material are integratedat the atomic level.

A method of manufacturing an electromagnetic noise suppressor of thepresent invention includes a vapor deposition process of physicallyvapor-depositing a magnetic material onto a binding agent to form acomposite layer on the surface of the binding agent. Such amanufacturing method enables it to easily manufacture theelectromagnetic noise suppressor of the present invention that has thecomposite layer constituted from the binding agent and the magneticmaterial integrated together.

A structure with an electromagnetic noise suppressing function of thepresent invention is a structure with at least a part of the surfacethereof covered by the electromagnetic noise suppressor of the presentinvention. The structure with an electromagnetic noise suppressingfunction enables it to dispose the electromagnetic noise suppressor in asmall space near a noise source and efficiently suppress electromagneticnoise in a sub-microwave band.

A method of manufacturing a structure with an electromagnetic noisesuppressing function of the present invention includes a coating processof coating at least a part of the surface of the structure with abinding agent, and a vapor deposition process of physicallyvapor-depositing a magnetic material onto the binding agent to form acomposite layer on the surface of the binding agent. Such amanufacturing method enables it to easily manufacture the structure withan electromagnetic noise suppressing function that can efficientlysuppress electromagnetic noise in a sub-microwave band.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an image of a composite layer of an electromagnetic noisesuppressor of the present invention observed with a high-resolutiontransmission electron microscope.

FIG. 2 is a schematic diagram showing the vicinity of the compositelayer in an example.

FIG. 3 is a perspective view of a camera module that is an example ofstructure with an electromagnetic noise suppressing function of thepresent invention.

FIG. 4 is a sectional view of a camera module that is an example ofstructure with an electromagnetic noise suppressing function of thepresent invention.

FIG. 5 is a sectional view of a printed wiring board having electroniccomponents mounted thereon that is an example of the structure with anelectromagnetic noise suppressing function of the present invention.

FIG. 6 is a graph showing the complex magnetic permeability versusfrequency in electromagnetic noise suppressor of Example 1.

FIG. 7 is a graph showing the complex magnetic permeability versusfrequency in electromagnetic noise suppressor of Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail.

<Electromagnetic Noise Suppressor>

The electromagnetic noise suppressor of the present invention hasmagnetic resonance frequency of 8 GHz or higher, and the imaginary partof complex magnetic permeability (μ″_(H)) at 8 GHz being higher than theimaginary part of complex magnetic permeability (μ″_(L)) at 5 GHz.

Complex magnetic permeability is expressed as μ=μ′−j μ″. μ′ is the realpart of the complex magnetic permeability and μ″ is the imaginary partof the complex magnetic permeability, that represents the magnetic lossrelated to the absorption of electromagnetic radiation.

The magnetic resonance frequency is a frequency at which the value ofthe real part μ′ of the complex magnetic permeability becomes one-halfof the peak value, and the frequency is higher than the peak frequency.The magnetic resonance frequency is regarded as the upper limit offrequencies at which noise current can be transformed into thermalenergy by means of the magnetic loss characteristic of the magneticmaterial.

In order for the electromagnetic noise suppressor of the presentinvention to fully demonstrate the electromagnetic noise suppressingeffect over the sub-microwave band, it is necessary that the magneticresonance frequency be 8 GHz or higher, and that the imaginary partμ″_(H) of complex magnetic permeability at 8 GHz be higher than theimaginary part μ″_(L) of complex magnetic permeability at 5 GHz, thatis, the imaginary part μ″ of complex magnetic permeability increasesmonotonically with the frequency. The magnetic resonance frequency ofthe electromagnetic noise suppressor of the present invention ispreferably 10 GHz or higher.

The magnetic resonance frequency of the electromagnetic noise suppressorof the present invention having a magnetic resonance frequency of 8 GHzor higher, and the imaginary part μ″_(H) of complex magneticpermeability at 8 GHz being higher than the imaginary part μ″_(L) ofcomplex magnetic permeability at 5 GHz can be made by forming thecomposite layer consisting of the magnetic material and part of thebinding agent being integrated with each other at the nanometer scale.

The composite layer is a layer formed by physical vapor deposition ofthe magnetic material on the binding agent, where the magnetic materialapplied by physical vapor deposition is dispersed in the binding agentand integrated therewith in the atomic state, without forming ahomogeneous film.

More specifically, as shown in the high-resolution transmission electronmicroscope image of FIG. 1 and the sketch of FIG. 2 which simplifies theelectron microscope image, the electromagnetic noise suppressor 1 isconstituted only from the composite layer 3 consisting of atoms of themagnetic material mixed with molecules of the binding agent 2, and alayer consisting only of the binding agent 2.

The composite layer 3 consists of a portion where crystal lattice 4 isobserved to be made up of atoms of the magnetic material disposed atspacing of several angstroms forming a very small crystal, a portionwhere only the binding agent 2 is observed without presence of themagnetic material in a very small region, and a portion where atoms ofthe magnetic material 5 are observed to be dispersed in the bindingagent without crystallizing. In other words, the magnetic material doesnot form fine particles having crystalline structure with clear grainboundary, but forms a complicated heterogeneous structure (a structurethat is not homogeneous nor uniform) where the binding agent and themagnetic material are integrated at the nanometer scale.

The thickness of the composite layer is the depth of infiltration of theatoms of the magnetic material into the surface layer of the bindingagent, that is dependent on such factors as the weight of the magneticmaterial deposited, kind of the binding agent and the conditions ofphysical vapor deposition, and is roughly in a range from 1.5 to 3 timesthe thickness of the magnetic material layer formed by the vapordeposition. When the thickness of the composite layer is set to be notless than 0.005 μm, atoms of the magnetic material and the binding agentcan be integrated in a dispersed state, giving rise to a high losscharacteristic in high frequency region due to the morphologicalanisotropy, thus achieving sufficient electromagnetic noise suppressingeffect. When the thickness of the composite layer exceeds 3 μm, on theother hand, a clear crystalline structure and then a homogeneous film ofthe magnetic material is formed to form a bulk magnetic material. Thisleads to a decrease in morphological anisotropy and less electromagneticnoise suppressing effect. Therefore, thickness of the composite layer ispreferably 1 μm or less, more preferably 0.3 μm or less.

Examples of the binding agent include, but are not limited to, organicmaterials, for example, resins such as polyolefine resin, polyamideresin, polyester resin, polyether resin, polyketone resin, polyimideresin, polyurethane resin, polysiloxane resin, phenol resin, epoxyresin, acrylic resin and polyacrylate resin; diene rubbers such asnatural rubber, isoprene rubber, butadiene rubber and styrene butadienerubber; non-diene rubbers such as butyl rubber, ethylene propylenerubber, urethane rubber and silicone rubber. The binding agent may alsobe of thermoplastic or thermosetting nature, or a material that has notyet been cured. The resin or rubber described above that is modified,mixed or copolymerized may also be used.

The binding agent may also be an inorganic material that has a lowelastic modulus in shear that will be described later, such as an aerogel or foamed silica that has high void ratio and such a level ofhardness that can capture ultra-fine particles. It may also be used inthe form of a composite material with the organic material describedabove.

The binding agent preferably has a low elastic modulus in shear in viewof the ease of atoms of the magnetic material to infiltrate into thebinding agent during the physical vapor deposition of the magneticmaterial. The elastic modulus in shear is preferably 5×10⁷ Pa or less. Adesirable value of elastic modulus in shear may be obtained by heatingthe binding agent to a temperature of 100 to 300° C., although thetemperature must be controlled so as not to decompose or vaporize thematerial. When physical vapor deposition is carried out at the normaltemperature, the binding agent is preferably an elastic material havinghardness of about 80° (JIS-A).

It is preferable that the binding agent have high elastic modulus inshear after being subjected to physical vapor deposition of the magneticmaterial, in order to maintain the heterogeneous structure describedpreviously. By processing the binding agent to have a high elasticmodulus in shear after physical vapor deposition of the magneticmaterial, it is made possible to surely prevent the atoms of themagnetic material or clusters thereof from aggregating and crystallizinginto fine particles on the nanometer scale. Specifically, the elasticmodulus in shear is preferably in a range from 1×10⁷ Pa or higher in atemperature range in which the electromagnetic noise suppressor is used.It is preferable to crosslink the binding agent after physical vapordeposition of the magnetic material, in order to obtain the desiredvalue of elastic modulus in shear.

In this regard, the binding agent is preferably a thermosetting resin ora resin that is cured when exposed to an energy beam (ultraviolet light,electron beam) which allows the elastic modulus to be low during vapordeposition and to be increased by crosslinking after the vapordeposition.

The binding agent may also include silane coupling agent, titanatecoupling agent, nonionic surfactant, polar resin oligomer or the like,so that part of the magnetic material that has been turned into plasmaor been ionized can react with the binding agent and be stabilized.Adding such an additive enables it to not only prevent oxidization butalso prevent a homogeneous film from being formed by the aggregation ofatoms so as to prevent the reflection of electromagnetic radiation bythe homogeneous film, thereby improving the absorbing property.

In addition to the above, the binding agent may also containreinforcement fillers, flame retarding agents, anti-aging agents,anti-oxidizing agents, colorants, thixotropy enhancing agents,plasticizers, lubricants and heat resistance enhancing agents. Careshould be exercised, however, since adding a hard material leads tocollision with the atoms of the magnetic material, thus resulting ininsufficient dispersion. Weatherability may also be improved by coatingwith silicon oxide or silicon nitride by vapor deposition, after thevapor deposition of the magnetic material.

The electromagnetic noise suppressor of the present invention may haveeither a planar configuration such as sheet or a three-dimensionalstructure. The shape may also be adapted to the shape of a structure tobe made as the product, when it is used to cover the surface of thestructure as will be described later.

<Method of Manufacturing the Electromagnetic Noise Suppressor>

The method of manufacturing the electromagnetic noise suppressor willnow be described.

The electromagnetic noise suppressor of the present invention can bemade by forming the composite layer on the surface of the binding agentby physical vapor deposition of the magnetic material onto the bindingagent.

In the physical vapor deposition (PVD), a material is vaporized in avacuum vessel and is deposited on a substrate that is placed in thevicinity of the material being vaporized, so as to form a thin film. Theprocess is classified by the method of evaporation into vaporizationprocess and sputtering process. Vaporization processes include EB vapordeposition and ion plating, and sputtering processes include highfrequency sputtering, magnetron sputtering and opposing target typemagnetron sputtering process.

In the EB vapor deposition, since the vapor particle has small energy of1 eV, less damage is caused on the substrate and the film tends tobecome porous and have insufficient strength, while the specificresistivity of the film increases.

In the ion plating process, since ions of argon gas and vaporizedparticles are accelerated and collide with the substrate, particleenergy is about 1 KeV, higher than in the case of EB. Therefore a filmhaving high adhesive force can be obtained, although it cannot beavoided that particles having sizes on the micrometer scale, calleddroplets, deposit on the surface and cause interruptions of discharge.An oxide film may be formed by introducing a reactive gas such asoxygen.

In the magnetron sputtering process, although the target (material to bevaporized) is utilized with less efficiency, growth rate is higher sincestrong plasma is generated by the effect of magnetic field and a highenergy of several tens of electron volts (eV) is given to the particle.In the high frequency sputtering process, an insulating target may beused.

Among the magnetron sputtering processes, the opposing target typemagnetron sputtering process is a process where plasma is generatedbetween opposing targets and is confined by the magnetic field, whilethe substrate is placed outside of the opposing targets so as to form adesired thin film without causing damage from the plasma. Therefore, afilm of the same composition as that of the target that is made of adense material can be formed without need to sputter the thin film ofthe substrate again and mitigating the collision of the sputtered atomswith further higher growth rate.

In the case in which the binding agent is a resin (or rubber), covalentbonding energy of the resin is about 4 eV. Bonding energies of C—C, C—H,Si—O and Si—C, for example, are 3.6 eV, 4.3 eV, 4.6 eV and 3.3 eV,respectively. In the ion plating, magnetron sputtering, or opposingtarget type magnetron sputtering process, in contrast, the vaporizedparticles have high energies and therefore may collide with the bindingagent and break part of the chemical bonding of the resin.

Therefore, it is supposed that, when the binding agent made of resin (orrubber) has a sufficiently low elastic modulus in the present invention,molecules of the resin vibrate and are sometimes broken when themagnetic material is deposited, resulting in localized mixing of theatoms of the magnetic material and the resin and, with the atoms of themagnetic material infiltrating into the resin to a depth of up to 3 μmfrom the surface, cause interaction with the resin, so that thecomposite layer having heterogeneous structure of nanometer scale isformed.

It is preferable to deposit the magnetic material with a particle energyof 5 eV or higher to the binding agent by physical vapor deposition,since it enables it to disperse a large amount of the magnetic materialin the binding agent at the same time. Since a large amount of themagnetic material can be processed in a single deposition run, theelectromagnetic noise suppressor having high electromagnetic noisesuppressing effect can be easily made. Since velocity of the bindingagent in vibration thereof is lower than the velocity of the particle,rate of vapor deposition is preferably set to be low in accordance tothe timing of relaxation of the binding agent, about 60 nm/min or lessdepending on the kind of magnetic material.

As the magnetic material to be vaporized in the vapor depositionprocess, a metal-based soft magnetic material, an oxide-based softmagnetic material and/or a nitride-based soft magnetic material ismainly used. Any one of these materials or a mixture of two or more ofthese materials may be used.

As the metal-based soft magnetic material, iron or an iron alloy iscommonly employed. As the iron alloy, Fe—Ni, Fe—Co, Fe—Cr, Fe—Si, Fe—Al,Fe—Cr—Si, Fe—Cr—Al, Fe—Al—Si or Fe—Pt alloy may be used. Any one ofthese materials or a mixture of two or more of these materials may beused. Either one of these metal-based soft magnetic materials or amixture of two or more of these materials may be used. Besides iron andiron alloy, cobalt, nickel or an alloy thereof may also be used. Nickelhas resistance against oxidation and is therefore preferably usedindependently.

As the oxide-based soft magnetic material, ferrite is preferably used.Specifically, MnFe₂O₄, CoFe₂O₄, NiFe₂O₄, CuFe₂O₄, ZnFe₂O₄, MgFe₂O₄,Fe₃O₄, Cu—Zn-ferrite, Ni—Zn-ferrite, Mn—Zn-ferrite, Ba₂Co₂Fe₁₂O₂₂,Ba₂Ni₂Fe₁₂O₂₂, Ba₂Zn₂Fe₁₂O₂₂, Ba₂Mn₂Fe₁₂O₂₂, Ba₂Mg₂Fe₁₂O₂₂,Ba₂Cu₂Fe₁₂O₂₂ or Ba₃Co₂Fe₂₄O₄₁, may be used. These variations of ferritemay be used either independently or in a combination of two more kindsthereof.

As nitride-based soft magnetic material, Fe₂N, Fe₃N, Fe₄N, Fe₁₆N₂, etc.,are known. These nitride-based soft magnetic materials have highmagnetic permeability and high corrosion resistance, and are thereforepreferably used.

During the physical vapor deposition of the magnetic material onto thebinding agent, since atoms of the magnetic material infiltrate into thebinding agent in the form of plasma or ions, the composition of themagnetic material dispersed in the binding agent is not necessarily thesame as that of the magnetic material before being vaporized. Themagnetic material may have reacted with part of the binding agent andchanged into paramagnetic material or antiferromagnetic material.

The amount of the magnetic material deposited on the binding agent in asingle deposition run is preferably 200 nm or less in terms of thicknessof the magnetic material layer. When deposited to a larger thickness,limitation of the capacity of the binding agent to include the magneticmaterial is reached such that the magnetic material cannot be dispersedin the binding agent any more and is instead deposited on the surface,thereby forming a continuous bulk film that has uniform conductivity.Therefore, the amount of the magnetic material to be deposited ispreferably 100 nm or less, and more preferably 50 nm or less. In view ofthe electromagnetic noise suppressing effect, the amount of the magneticmaterial to be deposited is preferably 0.5 nm or less.

Since less amount of deposition leads to lower electromagnetic noisesuppressing effect, the total amount of the magnetic material can beincreased by stacking a plurality of composite layers. The total amountof deposition is preferably in a range from 10 to 500 nm in terms oftotal thickness of the magnetic material, while it depends on therequired level of electromagnetic noise suppression. Part of the layersto be stacked may also be formed as bulk metal layers that havecontinuity, so as to have reflectivity to electromagnetic radiation. Thelayers may also be formed in composite structure with the dielectricmaterial layer so as to control the electromagnetic noise suppressingeffect.

While there is no restriction on the thickness of the binding agent usedin the vapor deposition process, it is preferably as small as possiblein order to make a compact electromagnetic noise suppressor.Specifically, the thickness is preferably 50 μm or less and morepreferably 10 μm or less.

<Structure with Electromagnetic Noise Suppressing Function>The structure with an electromagnetic noise suppressing function of thepresent invention is a structure with at least a part of the surfacethereof covered by the electromagnetic noise suppressor of the presentinvention.

The structure may be, for example, a printed wiring board havingelectronic components mounted thereon, a semiconductor integratedcircuit or the like.

Now specific examples of the structure with an electromagnetic noisesuppressing function of the present invention will be described below.

(Camera Module)

FIG. 3 and FIG. 4 show a camera module as an example of the structurewith an electromagnetic noise suppressing function. The camera moduleincludes a printed wiring board 12 that has an image sensor 11 mountedon the surface thereof, a lens 13 that corresponds to the image sensor11, a camera holder 14 that holds the lens 13 and encloses the imagesensor 11 on the printed wiring board 12, an outer case 15 that fits onthe outside of the camera holder 14, and the electromagnetic noisesuppressor 1 that covers the surface of the outer case 15.

Covering of the outer case 15 with the electromagnetic noise suppressor1 is carried out, for example, as follows. The outer case 15 that is astructure formed from a resin by injection molding is dipped in epoxyresin solution that is a binding agent so as to cover the surface withepoxy resin of B stage having a thickness of 15 μm. Then a compositelayer is formed on the epoxy resin by physical vapor deposition toequivalent thickness of 45 nm. The outer case 15 that is provided withthe electromagnetic noise suppressing function is fitted onto the cameraholder 14, thereby shielding the camera module from noise.

(Printed Wiring Board)

FIG. 5 shows a printed wiring board as another example of the structurewith an electromagnetic noise suppressing function. The printed wiringboard includes a circuit 22 formed on a substrate 21, a semiconductorpackage 23 and a chip component 24 that are connected to the circuit 22,and the electromagnetic noise suppressor 1 that covers the surface ofthe printed wiring board together with the circuit 22, the semiconductorpackage 23 and the chip component 24.

Covering of the printed wiring board with the electromagnetic noisesuppressor 1 is carried out, for example, as follows.

An insulating binding agent is applied to the printed wiring board to athickness of about 50 μm so as to cover the circuit 22, thesemiconductor package 23 and the chip component 24. The magneticmaterial is deposited onto the binding agent by physical vapordeposition so as to form the composite layer. This process is not a wetprocess and does not require washing operation to remove ions, and iscapable of easily rendering the electromagnetic noise suppressingfunction.

(Semiconductor Integrated Circuit)

To give electromagnetic noise suppressing function to a semiconductorintegrated circuit, the magnetic material is deposited to a thickness ofabout 10 to 50 nm by physical vapor deposition to form a composite layeron an organic insulating film having a thickness from 200 nm to 100 μmthat is formed from polyimide, polyparaxylene, polytetrafluoroethylene,polyaryl ether, polyxylylene, polyadamantane ether, polybenzo oxazole orbenzocyclobutene resin that has been formed on a semiconductor wafer byspin coating process or CVD (chemical vapor deposition). The compositelayer may also be formed partially by using a mask as required. Sincethis is a dry process, there is no influence of ionic impurity and thereis no need for cleaning, and the process is preferable for theapplication to semiconductor wafers. When the electromagnetic noisesuppressor having heterogeneous structure of nanometer scale is providedin the vicinity of microscopic semiconductor circuit, it is madepossible to suppress the resonance of a digital circuit during pulsetransmission and suppress radiation noise from being generated byimpedance mismatch, thereby to improving the transmissioncharacteristics such as transmission speed, even with a small amount ofmagnetic material.

The electromagnetic noise suppressor of the present invention describedabove has a high resonance frequency of 8 GHz or higher, supposedlybecause the composite layer is formed where the magnetic material andthe binding agent are integrated by physical vapor deposition so thateven a small amount of the magnetic material can achieve the quantumeffect originating from the heterogeneous structure of nanometer scale,magnetic anisotropy of the material, morphological magnetic anisotropyor anisotropy due to external magnetic field, although theoreticalexplanation has not been presented. It is considered that such a featureenables achievement of satisfactory magnetic characteristics andelectromagnetic noise suppressing effects over the entire sub-microwaveband with even a small amount of the magnetic material.

Since the electromagnetic noise suppressor of the present invention canachieve the electromagnetic noise suppressing effect even with a smallamount of the magnetic material, the amount of the magnetic material canbe reduced significantly, resulting in weight reduction.

Also, since the electromagnetic noise suppressor of the presentinvention can achieve sufficient electromagnetic noise suppressingeffect even with the composite layer having a thickness as small as 0.3μm or less, the electromagnetic noise suppressor can be formed with asmall thickness, so as to decrease the space requirement.

In the case in which the composite layer is formed by physical vapordeposition of the magnetic material onto the binding agent, the magneticmaterial is dispersed in the state of atoms into the binding agent sothat the magnetic material and the binding agent are integrated to formthe composite layer having high electromagnetic noise suppressing effectwith a small amount of the magnetic material. The composite layer doesnot include impurity ions so that there is no possibility of damage tothe electronic circuit by the impurity ions.

Since the amount of the magnetic material can be reduced significantly,decrease in flexibility and in strength of the resin or rubber due tothe magnetic material can be minimized in the case in which the bindingagent is resin or rubber.

Moreover, if the binding agent is a curable resin, the magnetic materialis distributed uniformly in the binding agent prior to curing and, afterbeing cured, the magnetic material can be suppressed from crystallizinginto fine particles even when the electromagnetic noise suppressor isused at a high temperature, thus improving the weatherability.

The structure with an electromagnetic noise suppressing function of thepresent invention (for example, printed wiring board or semiconductorintegrated circuit) enables it to dispose the noise suppressor withsmall space requirement in the vicinity of the noise source andefficiently suppress electromagnetic noise in the sub-microwave band.

EXAMPLES

Examples of the present invention will now be described.

(Evaluation)

The measurement of magnetic permeability: Ultra-high frequency magneticpermeability measuring instrument PMM-9G1 manufactured by RyowaElectronics Co., Ltd., was used. Observation of cross section: Crosssection was observed with a transmission electron microscope H9000NARmanufactured by Hitachi, Ltd.

Electromagnetic radiation absorbing characteristic: Transmission noisesuppressing effect was evaluated by S parameter method using testfixture TF-3A, TF-18A for micro strip line having impedance of 50Ωmanufactured by KEYCOM Corporation.

Coupling coefficient in near field was evaluated using micro loopantenna type fixture manufactured by KEYCOM Corporation. Vector networkanalyzer 37247C manufactured by Anritsu Company was used.

Example 1

A silicone rubber that had been vulcanized having a thickness of 15 μm(elastic modulus in shear of 1×10⁷ Pa at normal temperature containingwet silica) was provided as the binding agent on a polyethylenephthalate film used as the support layer having a thickness of 12 μm(elastic modulus in shear of 3.8×10⁹ Pa at the normal temperature), andthereon a composite layer was formed by sputtering Fe—Ni-based softmagnetic metal to an equivalent thickness of 20 nm by physical vapordeposition of the opposing target type magnetron sputtering process,thereby to obtain the electromagnetic noise suppressor. Sputtering wascarried out by applying a low negative voltage so as to impart energy of8 eV to the vaporized particles while maintaining the substrate at thenormal temperature.

Then a thin portion was sliced by means of a microtome from theelectromagnetic noise suppressor thus obtained and, after polishing thecut surface by ion beam, cross section of the composite layer wasobserved with a high-resolution transmission electron microscope. Thethickness of the composite layer was about 45 nm. The cross section thusobserved is shown in FIG. 1. Magnetic permeability was measured with amagnetic permeability measuring instrument. As shown in FIG. 6, relativeintensity of μ″_(L) was 250 and relative intensity of μ″_(H) was aboutseven times the value described above. The magnetic resonance frequency(the frequency at which the value of μ′ becomes one-half of the peakvalue, and which is higher than the peak frequency) exceeded 9 GHz, themeasurement limit of the instrument. The measurement of theelectromagnetic radiation absorbing characteristics showed thatreflection attenuation was −9.5 dB and transmission attenuation was −5.5dB at 1 GHz, while reflection attenuation was −14 dB and transmissionattenuation was −20 dB at 10 GHz.

Example 2

An epoxy resin of B stage having a thickness of 25 μm (elastic modulusin shear of 8×10⁶ Pa before curing and elastic modulus in shear of 2×10⁹after curing) was provided as the binding agent on a polyethyleneterephthalate film that had been subjected to mold-release treatment andused as the support layer having a thickness of 12 μm, and thereon acomposite layer was formed by depositing Fe—Ni-based soft magnetic metalto an equivalent thickness of 10 nm by physical vapor deposition of theopposing target type magnetron sputtering process. Sputtering wascarried out by applying a low negative voltage so as to impart energy of8 eV to the vaporized particles while maintaining the substrate at thenormal temperature. The epoxy sheet was removed from the polyethylenephthalate film and was cut into halves, and the epoxy sheet were placedon the other so that the composite layers were stacked alternately. Thestack was heated to 40° C. for 6 hours then 120° C. for 2 hours so as toharden the epoxy resin, thereby to obtain the electromagnetic noisesuppressor. As shown in FIG. 7, relative intensity of μ″_(L) was 200 andrelative intensity of μ″_(H) was about five times the value describedabove. The magnetic resonance frequency (the frequency at which thevalue of μ′ becomes one-half of the peak value, and which is higher thanthe peak frequency) exceeded 9 GHz, the measurement limit of theinstrument. The measurement of the electromagnetic radiation absorbingcharacteristics showed that internal coupling coefficient was −8 dB andmutual coupling coefficient was −7 dB at 3 GHz.

Example 3

Metal Ni was deposited to a thickness of 30 nm on one side of apolyimide film used as the support layer having a thickness of 12 μm,and provided on the other side was vulcanized electrically conductivesilicone rubber having a thickness of 7 μm (elastic modulus in shear of2×10⁷ Pa at the normal temperature with 15% by weight of carbon blackincluded) as the binding agent. Then composite layers were formed on thetop and bottom surfaces by depositing a Fe—Ni-based soft magnetic metalto equivalent thickness of 20 nm by physical vapor deposition ofopposing target type magnetron sputtering process, thereby to obtain anelectromagnetic noise suppressor. Sputtering was carried out by applyinga low negative voltage so as to impart energy of 8 eV to the vaporizedparticles while maintaining the substrate at the normal temperature.Relative intensity of μ″_(L) of the imaginary part of the complexmagnetic permeability was 180 and relative intensity of μ″_(H) was aboutsix times the value described above. The magnetic resonance frequency(the frequency at which the value of μ′ becomes one-half of the peakvalue, and which is higher than the peak frequency) exceeded 9 GHz, themeasurement limit of the instrument. The measurement of theelectromagnetic radiation absorbing characteristics showed that internalcoupling coefficient was −3 dB and mutual coupling coefficient was −4 dBat 1 GHz.

Example 4

An epoxy resin of B stage containing NBR (elastic modulus in shear of8×10⁶ Pa before curing and elastic modulus in shear of 8×10⁸ Pa aftercuring) was provided as the binding agent on a metallic conductor formedon a polyimide film with wiring pitch of 0.3 mm, and thereon a compositelayer was formed by depositing Fe—Ni-based soft magnetic metal to anequivalent thickness of 15 nm by physical vapor deposition of theopposing target type magnetron sputtering process. Sputtering wascarried out by applying a low negative voltage so as to impart energy of8 eV to the vaporized particles while maintaining the substrate at thenormal temperature. The sample was heated to 40° C. for 6 hours then120° C. for 2 hours so as to harden the epoxy resin, thereby to obtain aprinted wiring board having the electromagnetic noise suppressorprovided thereon.

The wiring board, an LCD (controller LSI is provided on glass) and a CPUof a mobile telephone were connected with each other. Display of movingpicture was compared with one that was not provided with theelectromagnetic noise suppressor, and the Example showed a display thatwas not influenced by crosstalk without faulty signal compared to thatwithout the electromagnetic noise suppressor.

INDUSTRIAL APPLICABILITY

The electromagnetic noise suppressor of the present invention can beused to cover electronics apparatus and electronic components, andenables the manufacture of electronic apparatuses and electroniccomponents that are smaller and lighter in weight while achievingsufficient electromagnetic noise suppressing effect over entire thesub-microwave band.

1. A method of manufacturing an electromagnetic noise suppressor, themethod comprising: physically vapor-depositing a magnetic material ontoa binding agent to form a composite layer on the surface of the bindingagent, thus obtaining an electromagnetic noise suppressor having amagnetic resonance frequency of 8 GHz or higher, and the imaginary partμ″_(H) of complex magnetic permeability at 8 GHz higher than theimaginary part μ″_(L) of complex magnetic permeability at 5 GHz.
 2. Amethod of manufacturing a structure with an electromagnetic noisesuppressing effect, the method comprising: coating at least a part ofthe surface of the structure with a binding agent; and physicallyvapor-depositing a magnetic material onto the binding agent to form acomposite layer on the surface of the binding agent.